THE COQ7 GENE ENCODES A PROTEIN IN SACCHAROMYCES-CEREVISIAE NECESSARYFOR UBIQUINONE BIOSYNTHESIS

Ubiquinone (coenzyme Q) is a lipid that transports electrons in the re spiratory chains of both prokaryotes and eukaryotes. Mutants of Saccha romyces cerevisiae deficient in ubiquinone biosynthesis fail to grow o n nonfermentable carbon sources and have been classified into eight co mplementation groups (coq1-coq8; Tzagoloff, A., and Dieckmann, C. L. ( 1990) Microbiol. Rev. 54, 211-225). In this study we show that althoug h yeast coq7 mutants lack detectable ubiquinone, the coq7-1 mutant doe s synthesize demethoxyubiquinone 2-hexaprenyl-3-methyl-6-methoxy-1,4-b enzoquinone), a ubiquinone biosynthetic intermediate. The correspondin g wild-type COQ7 gene was isolated, sequenced, and found to restore gr owth on nonfermentable carbon sources and the synthesis of ubiquinone, The sequence predicts a polypeptide of 272 amino acids which is 40% i dentical to a previously reported Caenorhabditis elegans open reading frame. Deletion of the chromosomal COQ7 gene generates respiration def ective yeast mutants deficient in ubiquinone. Analysis of several coq7 deletion strains indicates that, unlike the coq7-1 mutant, demethoxyu biquinone is not produced. Both coq7-1 and coq7 deletion mutants, like other coq mutants, accumulate an early intermediate in the ubiquinone biosynthetic pathway, 3-hexaprenyl-4-hydroxybenzoate. The data sugges t that the yeast COQ7 gene may encode a protein involved in one or mor e monoxygenase or hydroxylase steps of ubiquinone biosynthesis.